In general, in a case of coating vehicle bodies of automobiles, articles of furniture, electrical appliances, and the like with paint, a rotary atomizing head type coating machine that is excellent in a coating efficiency and coating finish of paint is used. An example of the rotary atomizing head type coating machine includes an electrostatic coating machine that applies high voltages to paint to be supplied to a rotary atomizing head. In this example, paint particles charged with the high voltage can fly along an electrical line of force formed between a coated object and the rotary atomizing head, being efficiently applied on the coated object.
This rotary atomizing head type coating machine is configured of an air motor that uses compressed air as a power source, a hollow rotational shaft that is rotatably supported by the air motor and a front end of which protrudes to a front side from the air motor, a feed tube that extends to the front end of the rotational shaft through the rotational shaft to supply the paint, a rotary atomizing head that is mounted to the front end of the rotational shaft and is provided with an outer peripheral surface expanding in a cup shape to a front side, an inner peripheral surface for dispersing the paint supplied from the feed tube and a releasing edge positioned at a front end side to release the paint, and a shaping air ring that is disposed on the outer periphery of the rotary atomizing head such that a front end thereof is positioned closer to the backward than the releasing edge of the rotary atomizing head.
The shaping air ring has first shaping air ejecting holes that eject shaping air toward the releasing edge of the rotary atomizing head and second shaping air ejecting holes that eject shaping air along an outer peripheral surface of the rotary atomizing head.
The shaping air ring ejects the shaping air from the first and second shaping air ejecting holes respectively to micronize the paint sprayed from the releasing edge of the rotary atomizing head, while adjusting a spray pattern of paint particles to a desired size and shape. Further, the shaping air ejecting hole is inclined to a direction reverse to a rotational direction of the rotary atomizing head. Therefore, the shaping air ejected from the shaping air ejecting hole can collide squarely with liquids of the paint flying in a tangential direction from the rotary atomizing head to efficiently micronize the paint. In addition to the above, speeding up a flow velocity of the shaping air accelerates the micronization of the paint (Patent Document 1).
Here, an example of the method of speeding up the flow velocity of the shaping air includes a method of reducing a diameter of the shaping air ejecting hole to be small to increase the ejecting holes in number. This method can accelerate the micronization of the paint to finely control the spray pattern. However, since an advanced processing technique is required for microscopic hole drilling, in a case of reducing the diameter of the shaping air ejecting hole to be small and increasing the ejecting holes in number, manufacturing costs of the shaping air ring are increased. Further, in a case of increasing the shaping air ejecting holes in number, since a consumption amount of compressed air increases, an air compressor as a supply source of the compressed air is required to largely increase in size, leading to a problem of an increase in equipment cost.
In addition, a negative pressure region is generated in the surroundings of the shaping air ejecting hole in the shaping air ring due to the ejection of the shaping air having a fast flow velocity. As a result, since a part of the sprayed paint particles is pulled to the negative pressure region to be gradually attached to the front end of the shaping air ring, a periodical cleaning work is required to maintain coating quality of the shaping air ring. In this cleaning work, the shaping air ejecting holes formed as microscopic holes in addition to a front end part of the shaping air ring are required to be cleaned one by one, leading to necessity of lots of labors for the cleaning work to increase running costs.
It should be noted that the shaping air ring is generally formed of a material that is light in weight and excellent in workability, such as an aluminum alloy, and a surface thereof is subjected to corrosion resistance plate processing. Accordingly, an ultrasound bath that is effective in washing precision components cannot be currently used for avoiding separation of the plate.
On the other hand, there is an example of a rotary atomizing head type coating machine using another conventional technology, in which a shaping air ring is configured of an annular air nozzle and an annular cap that is disposed on an outer peripheral side of the air nozzle. According to this shaping air ring, numerous spiral grooves are disposed on an outer peripheral surface of the air nozzle in a position deeper than a front end of the shaping air ring, and outer peripheral sides of these spiral grooves are covered with an inner peripheral surface of the cap. Therefore, numerous shaping air ejecting holes that eject the shaping air are formed between each of the spiral grooves and the inner peripheral surface of the cap. In this case, not unworkable hole drilling but easy-to-work grooving can be used for forming each of the shaping air ejecting holes (Patent Document 2).